Charging control apparatus controlling charging current and control method therefore

This application claims the benefit of Japanese Patent Application No. 2007-323924 filed on Dec. 14, 2007 in the Japanese Patent Office, and Application No. 2008-002095 filed on Jan. 9, 2008 in the Japanese Patent Office, the disclosure of which is herein incorporated in its entirety by reference.

The technology relates to a charging control technique for a battery.

A secondary battery having an upper limit of charging voltage is equipped with a protection circuit that monitors battery voltage so as to prevent overcharge of the battery and that stops the charging operation if the battery voltage exceeds the upper limit voltage.

Further, the charging operation of the secondary battery is performed by using a charging circuit. The charging circuit is a constant current and constant voltage circuit, which can control charging current and charging voltage. In this case, charging control is performed so that the charging voltage does not exceed a predetermined upper limit voltage.

However, monitoring of the battery voltage by the protection circuit and monitoring of the charging voltage by the charging circuit may have an error. Therefore, although the charged state is not actually a full charge state, the charging operation may be stopped due to errors in the protection circuit and the charging circuit, resulting in an insufficient charged state.

It is an object of the technology to provide a charging control technique that enables to charge a secondary battery to be a desired charged state by reducing the influence of a detection error as described above when the secondary battery having a protection circuit is charged.

In order to solve the above problems, the technology employs a structure described below. In one aspect of the technology, a control apparatus for a battery circuit that includes a voltage detector that detects a battery voltage, a battery protection circuit that stops charging current when the battery voltage detected by the voltage detecting unit exceeds a protection voltage, and a charging circuit being capable of changing a charging current value for charging a battery will be described. The control apparatus includes an input interface that reads the battery voltage detected by the voltage detecting unit, a decision unit that decides whether or not the read battery voltage has approached the protection voltage to a predetermined limit value, an output interface that outputs a signal for controlling the charging current, and a current control unit that limits the charging current to a predetermined limit value via the output interface when the read battery voltage is decided to have approached the protection voltage to the predetermined limit value.

According to this structure, the charging current is restricted in the state where the battery voltage is close to a protection voltage. Thus, it is possible to avoid as much as possible a situation where the battery voltage exceeds the protection voltage so that the charging current is stopped.

Here, the battery is made up of a plurality of cell blocks connected in series, each of which includes one cell or a plurality of cells, and the voltage detecting unit may include a measuring circuit that detects a voltage of each of the cell blocks. As a result, the decision unit decides whether or not a voltage of any one of the cell blocks has approached the protection voltage of the cell block to the predetermined limit value, and the current control unit only needs to limit the charging current if the voltage of any one of the cell blocks is decided to have approached the protection voltage of the cell block to the predetermined limit value. According to this structure, it is possible to decide whether or not a voltage of each cell block has approached the protection voltage of the cell block to the predetermined limit value. In other words, it can be decided whether or not the charging current should be limited based on a voltage of not the entire battery but each of the cell blocks.

In another aspect of the technology, a control apparatus for a battery circuit that includes a voltage detector that detects a battery voltage, a battery protection circuit that stops charging current when the battery voltage detected by the voltage detecting unit exceeds a protection voltage, and a charging circuit being capable of changing a charging current value for charging a battery, may include an input interface that inputs a signal indicating an operating state of the battery protection circuit, an output interface that outputs a signal for controlling the charging current, a protection state decision unit that decides whether or not the battery protection circuit has stopped the charging current, a voltage state decision unit that decides whether or not the battery voltage has reached the protection voltage, after the battery protection circuit stopped the charging current, and a charging control unit that cancels a stopping process of the charging current performed by the battery protection circuit and restarts the charging with the charging current limited to a predetermined limit value via the output interface when the battery voltage has not reached the protection voltage. In other words, if the battery voltage has not reached the protection voltage after the battery protection circuit stopped the charging current once, the stopping process of the charging current performed by the battery protection circuit is cancelled and the charging is restarted with the charging current limited to a predetermined limit value via the output interface, and hence the charging for the battery can be continued as long as possible.

In addition, another aspect may be a charging control apparatus that is a combination of the control apparatus and the battery circuit. Still another aspect may be an electronic device that is a combination of the battery, the charging control apparatus and a load.

Thus, when the secondary battery equipped with the protection circuit is charged, an influence of the detection error as described above can be reduced so as to increase a possibility of charging the secondary battery to a desired charged state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a hardware structure of an electronic device.

FIG. 2 is a block diagram illustrating an example of a structure of a charging circuit.

FIG. 3 illustrates an example of an operation of a charging control apparatus.

FIG. 4 is a diagram illustrating a conventional control sequence performed by a microcomputer.

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